1. Field of the Invention
The present invention relates to an insulating-film forming material, more precisely, to that capable of forming a coating film having a suitable uniform thickness, as an interlayer insulating-film material for semiconductor devices and others, and the film cracks little and has good dielectric characteristics. In particular, the insulating-film forming material of the invention is suitable for forming porous. insulating films.
2. Description of the Related Art
Heretofore, silica (SiO2) films formed in a vacuum process such as CVD are much used for interlayer insulating films in semiconductor devices and others. In recent years, insulating films that comprise, as the essential ingredient thereof, a hydrolyzed product of tetraalkoxysilane are formed in a coating process for more uniform interlayer insulating films, and they are referred to as SOG (spin on glass) films. With the increase in the degree of integration of semiconductor devices and others, organic SOG films have been developed for solving the problem of wiring delay. Comprising polyorganosiloxane as the essential ingredient thereof, the films serve as interlayer insulating films having a low dielectric constant.
CVD-SiO2 films have a lowest dielectric constant of all inorganic material films, but their dielectric constant is about 4 or so. SiOF films have been investigated as CVD films having a low dielectric constant, and their dielectric constant is from about 3.3 to 3.5. However, the moisture absorption of the films is high, and the films are therefore problematic in that their dielectric constant may increase while they are used.
On the other hand, organic polymer films having a low dielectric constant of from 2.5 to 3.0 have a low glass transition temperature falling between 200 and 350° C. and have a large coefficient of thermal expansion, and are therefore problematic in that they may damage wiring. Organic SOG films are defective in that they may be readily oxidized and cracked in oxygen plasma ashing for resist peeling in multi-layered wiring pattern formation. Organic resins including organic SOG films are poorly adhesive to wiring materials, aluminium and aluminium-based alloys as well as copper and copper-based alloys, and are therefore problematic in that they may form voids around wires (concretely between wires and insulating material therearound). Water may penetrate into the voids to cause wire corrosion, and, in addition, the voids around wires may cause short circuits between wiring layers when via holes formed for multi-layered wiring are mispositioned, and, as a result, it lowers the reliability of the wired devices.
In that situation, known is an insulating-film forming, coating composition that contains a basket-structured organopolysiloxane, concretely an octasilsesquioxane hydride-containing copolymer, as an insulating-film material that has good insulating properties, heat resistance and durability (see JP-A 2000-265065 and JP-A 2000-265066). JP-A 11-40554 discloses an insulating-film forming, coating composition that contains a T8 basket-structured siloxane (silsesquioxane), and it says that, when an insulating film of low density is formed through crosslinking polymerization, then the dielectric constant-of the film may be reduced.